Fluid-Structure Interaction, Pair
The Fluid-Structure Interaction, Pair () multiphysics node provides a coupling between a pair of boundaries, where one is the boundary of a fluid domain and the other is part of solid structure. The solid material can be modeled either in a neighboring domain or on the boundary itself. In the former case, the Solid Mechanics or Multibody Dynamics interface is used; in the latter, one of the Shell or Membrane interfaces is used.
You need to use this type of coupling if the geometry sequence is set up to form an assembly. In the more common case of a union when the boundary is shared, use the Fluid-Structure Interaction multiphysics coupling.
The effect of the coupling depends on whether a Deforming Domain is active in the fluid domain or not. For cases when the structural deformations are so small that the change in the geometry of the fluid can be ignored, you do not have to use a deforming domain. This is called a fixed geometry. Domains with a fixed geometry have fewer degrees of freedom and are less nonlinear and are thus computationally less expensive
If Deforming Domain is active in any domain, the Include geometric nonlinearity option is automatically selected in all applicable study nodes.
Settings
The Label is the multiphysics coupling feature name. The default Label (for the first multiphysics coupling feature in the model) is Fluid-Structure Interaction, Pair 1.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is fsip1.
Boundary Selection
The boundary selection cannot be edited manually. The contents are obtained from the Pair Selection.
Coupled Interfaces
This section defines the physics interfaces involved in the Fluid-Structure Interaction coupling. The Fluid and Structure lists include all applicable physics interfaces.
The default values depend on how the node is created.
If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (macOS and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
If it is added automatically when the physics interface is chosen in the Model Wizard or Add Physics window, then the two participating physics interfaces are selected.
You can also select None from either list to uncouple the Fluid-Structure Interaction, Pair node from a physics interface. If the physics interface is removed from the Model Builder, for example Solid Mechanics is deleted, then the Structure list defaults to None as there is nothing to couple to.
If a physics interface is deleted and then added to the model again, then in order to re-establish the coupling, you need to choose the physics interface again from the lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present physics interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.
Pair Selection
Select pairs for which this coupling is to be used. The pairs must be defined under Definitions in the component.
Fixed Geometry
In the case when the coupling is of the fixed geometry type, you can select which aspect of the interaction you want to model. From the Fixed geometry coupling type list, select Fully coupled, Fluid loading on structure, or Velocity transmission to fluid.
In the case Fluid loading on structure, pressure and viscous forces in the fluid affect the structure, but the structure does not affect the fluid flow.
In the case Velocity transmission to fluid, the structural velocity acts as boundary condition for the fluid, but the fluid does not affect the structure.
For Fully coupled, both effects are taken into account.
When a boundary is adjacent to an active deforming domain, the settings is this section are ignored.